The present invention relates to novel pigments, and in particular, pigments that have been treated with certain organo-phosphoric acid compounds and/or their salts.
The incorporation of pigments into polymer matrices has been performed for many years, and over the years, pigments have been and continue to be incorporated into polymer matrices for many reasons. For example, pigments may be used as fillers. They may also be used to impart better physical and chemical attributes to polymer matrices, including improved thermal stability, especially lacing resistance in extruded polymer film applications, and decreased chemical activity. In order to obtain different benefits, pigments may be treated in different ways, including by adding surface treatments.
Commonly used pigments include titanium dioxide, kaolin and calcium carbonate. Commonly known surface treatments that have been applied to pigments include silanes, alkylphosphonic acids and phosphorylated polyenes.
The precise attributes that one wants in a treated pigment will depend in part on the application in which it will be used. Often one wants to provide a hydrophobic pigment that is stable, easy to prepare, cost effective, can be dispersed to a high degree in polymers, and does not react in the presence of other additives such as lithopone. However, despite the numerous known surface treatments, for various reasons, including cost and desired properties, no known surface treatments are ideal for all applications. Thus, there is always a need to develop new and better treatments for pigments.
One under-explored option for treating pigments is the use of organo-phosphoric acids, including the esters of phosphoric acids and their corresponding salts. These compounds have been suggested as useful when mixed in relatively large amounts with pigments and to form suspensions in, for example, aqueous coatings applications. However, such a use produces a unique product that may be used only in a limited application. Thus, the teachings for the use of relatively large amounts of esters of phosphoric acids in aqueous coatings applications do not suggest the treatment of pigments with low levels of the organo-phosphoric acids of this invention or that the pigments treated with the low levels of the organo-phosphoric acids of this invention would have utility in plastics.
The present invention provides economical and easily prepared novel pigments that possess resistance to lacing when incorporated into polymeric articles (such as films), do not produce objectionable side reactions when mixed with common plastics additives such as lithopone, which contains zinc sulfide, and are stable such that they possess low levels of extractable organics. Further, durable plastics products that incorporate the treated pigments of the present invention are likely to resist yellowing when phenolic-type antioxidants are used.
The present invention provides novel treated pigments for use in polymer matrices. According to the present invention, pigmentary bases are treated with one or more organo-phosphoric acid compounds and/or their salts in order to form treated pigments.
In one embodiment, the treated pigment comprises a pigmentary base that may be treated with the reaction products of: (1) at least one organic alcohol; and (2) P2O5 and/or phosphoric acid. The phrases xe2x80x9cat least one organic alcoholxe2x80x9d and xe2x80x9corganic alcoholsxe2x80x9d mean one or more types of organic alcohols, for example, a solution of hexanol or octanol or a mixture of hexanol and octanol. The organic alcohols, P2O5 and phosphoric acid are selected such that their reaction products include an organo-acid phosphate that may be represented by the formula:
(Rxe2x80x94O)xPO(OH)yxe2x80x83xe2x80x83Formula 1
wherein
x=1 or 2;
y=3xe2x88x92x; and
R is an organic group having from 2 to 22 carbon atoms.
Alternatively, one may start with the organo-acid phosphate or its corresponding salt directly if it is available, rather than produce it from the reactants described above.
In another embodiment, the present invention provides for a pigment treated with an organopyrophosphate or an organopolyphosphate and/or their corresponding salts. The organopyrophosphate and organopolyphosphate compounds may be represented by the formula:
Rxe2x80x2nxe2x88x92P(nxe2x88x922)O4+[3(nxe2x88x923)]xe2x80x83xe2x80x83Formula 2
wherein
n=4-14; and
each Rxe2x80x2 is an organic group having from 2 to 22 carbon atoms or hydrogen and within any one molecule, any two or more Rxe2x80x2 groups may be the same provided that at least one of the Rxe2x80x2 groups is not hydrogen.
In still another embodiment, the present invention provides for a treated pigment comprised of a pigmentary base that has been treated with an organometaphosphate compound and/or its corresponding salt wherein the organometaphosphate compound may be represented by the formula:
(Rxe2x80x3PO3)mxe2x80x83xe2x80x83Formula 3
wherein
m=1-14, and each Rxe2x80x3 is an organic group having from 2 to 22 carbon atoms or hydrogen and within any one molecule, any two or more Rxe2x80x3 groups may be the same provided that at least one of the Rxe2x80x3 groups is not hydrogen. Collectively, the group of compounds represented by Formulas 1-3, i.e., the organo-acid phosphate, the organopolyphosphate, the organopyrophosphate and the organometaphosphate are referred to herein as xe2x80x9corgano-phosphoric acids.xe2x80x9d
The treated pigments of the present invention may be combined with and readily dispersed into polymers to form polymer matrices. For example, the pigments of the present invention may be incorporated into a polymer matrix containing up to about 85% of organo-phosphoric acid treated titanium dioxide pigment, based on the weight of the polymer matrix to be produced. The polymer matrix may be an end-product in and of itself or a product that will be further processed such as in a masterbatch, which can be let down into a polymeric film. These polymer matrices have improved physical properties such as impact strength, tensile strength and flexural characteristics.
The treated pigments of the present invention may also be used to prepare highly loaded polymer masterbatches. These highly loaded masterbatches are especially useful in applications in which dispersion and thermal stability, especially resistance to lacing, are critical.
The treated pigments of the present invention have the advantages of being pigments that are stable, easy to prepare, cost effective, can be dispersed to a high degree in polymers, and do not react in the presence of other additives such as lithopone. Such treated pigments may be useful in the manufacture of plastics and other products.
The present invention provides novel pigments for use in connection with polymers and offers several benefits over currently used pigments. According to the present invention, pigmentary bases are treated with an organo-phosphoric acid that may be an organo-acid phosphate, an organopyrophosphate, an organopolyphosphate or an organometaphosphate, or a salt of any of the aforementioned compounds. The pigmentary bases may also be treated with mixtures of any of the aforementioned compounds and/or their salts. The resulting treated pigments may then be combined with polymers to form novel polymer matrices.
The present disclosure is not intended to be a treatise on either pigments or the production of polymer matrices. Readers are referred to appropriate, available texts and other materials in the field for additional and detailed information on any aspect of practicing this invention.
Suitable pigmentary bases for use in the present invention include titanium dioxide, kaolin, talc, mica and calcium carbonate. The phrase xe2x80x9cpigmentary basexe2x80x9d as used herein refers to the pigment that has not been treated with an organo-phosphoric acid compound. Preferably, titanium dioxide is the chosen pigmentary base. When the pigmentary base is titanium dioxide, the titanium dioxide may be either rutile or anatase, both of which may be produced by processes that are well known to those skilled in the art. For certain applications, it may be desirable to pre-treat the pigmentary base with inorganic oxides or other compounds prior to the addition of the organo-phosphoric acid compound in order to alter the attributes of the final product or to facilitate production.
Under the first embodiment, one treats the pigmentary base with an organo-acid phosphate, which may be formed from the reaction of organic alcohols, and P2O5 and/or phosphoric acid. The organic alcohols useful in the present invention may have hydrocarbon groups from about 2 to about 22 carbon atoms. These hydrocarbons may be linear or branched, substituted or unsubstituted, and saturated or unsaturated. Some examples of the organic alcohols suitable for use in the present invention include, ethanol, propanol, butanol, isobutanol, tertiary butanol, pentanol, hexanol, heptanol, octanol, isooctanol, 2-ethylhexanol, decanol, dodecanol and the like. Preferably, the alcohol is a linear hexanol, a linear octanol, isooctanol or 2-ethylhexanol. The alcohol may be combined with either or both P2O5 and phosphoric acid. The conditions under which to react these materials in order to form the organo-acid phosphate are generally known or knowable to those skilled in the art.
Rather than beginning with the organic alcohols and P2O5 and/or phosphoric acid, one may start directly with the organo-acid phosphate of the below formula:
(Rxe2x80x94O)xPO(OH)yxe2x80x83xe2x80x83Formula 1
wherein
x=1 or 2;
y=3xe2x88x92x; and
R is an organic group having from 2 to 22 carbon atoms.
The phrase xe2x80x9corgano-acid phosphatexe2x80x9d as used herein refers to a compound that may be represented by Formula 1. In the organo-acid phosphate of Formula 1, the organic groups may be linear or branched, substituted or unsubstituted, and saturated or unsaturated. Preferably R is a linear hexyl- or octyl-aliphatic group or a branched hexyl- or octyl-aliphatic group. The use of hexyl-, octyl- or ethylhexyl-aliphatic groups will result in excellent pigmentary performance.
In a second embodiment, the present invention provides for a treated pigment that comprises a pigmentary base that has been treated with an organo-phosphoric acid compound that is either an organopyrophosphate or organopolyphosphate. These compounds may be represented by the formula:
Rxe2x80x2nxe2x80x94Pnxe2x88x922)O4+[3(nxe2x88x923)]xe2x80x83xe2x80x83Formula 2
wherein
n=4-14; and
each Rxe2x80x2 is an organic group having from 2 to 22 carbon atoms or hydrogen and within any one molecule, any two or more Rxe2x80x2 groups may be the same provided that at least one of the Rxe2x80x2 groups is not hydrogen.
The symbol Rxe2x80x2 as used in Formula 2 denotes any organic group that contains from 2 to 22 carbon atoms or hydrogen. Within any molecule the Rxe2x80x2 groups may all be the same moiety or they may be different moieties. These organic groups may be linear or branched, substituted or unsubstituted, and saturated or unsaturated. If the Rxe2x80x2 groups are all the same moieties, then they cannot be hydrogen. Preferably at least one of the Rxe2x80x2 groups is hydrogen and at least one of the Rxe2x80x2 groups will be linear hexyl or octyl aliphatic groups or branched hexyl or octyl aliphatic groups. Examples of organopyrophosphate acid compounds and organopolyphosphate acid compounds include caprylpyrophosphate, 2-ethylhexylpyrophosphate, dihexylpyrophosphate, dihexylammoniumpyrophosphate, dioctylpyrophosphate, diisooctylpyrophosphate, dioctyltriethanolaminepyrophosphate, bis(2-ethylhexyl)pyrophosphate, bis(2-ethylhexyl) sodium pyrophosphate, tetraethylpyrophosphate, tetrabuytlpyrophosphate, tetrahexylpyrophosphate, tetraoctylpyrophosphate, pentahexyltripolyphosphate, pentaoctyltripolyphosphate, tetrahexyl sodium tripolyphosphate, tetrahexylammoniumtripolyphosphate, pentahexyl sodium tetrapolyphosphate, trioctyl sodium tetrapolyphosphate, trioctyl potassium tetrapolyphosphate, hexabutyltetrapolyphosphate, hexahexyltetrapolyphosphate and hexaoctyltetrapolyphosphate.
In a third embodiment, the present invention provides for a treated pigment comprised of a pigmentary based that has been treated with an organometaphosphate compound wherein the organometaphosphate compound may be represented by the formula:
(Rxe2x80x3PO3)mxe2x80x83xe2x80x83Formula 3
wherein
m=1-14, and each Rxe2x80x3 is an organic group having from 2 to 22 carbon atoms or hydrogen and within any one molecule, any two or more Rxe2x80x3 groups may be the same provided that at least one of the Rxe2x80x3 groups is not hydrogen.
The symbol Rxe2x80x3 as used in Formula 3 denotes any organic group that contains from 2 to 22 carbon atoms or hydrogen. These organic groups may be linear or branched, substituted or unsubstituted, and saturated or unsaturated. xe2x80x9cmxe2x80x9d may be from about 1 to about 14, and preferably xe2x80x9cmxe2x80x9d is from about 4 to about 14. Within any molecule, the Rxe2x80x3 groups may all be the same moiety or they may be different moieties. If the Rxe2x80x3 groups are all the same moieties, then they cannot be hydrogen. Preferably at least one of the Rxe2x80x3 groups will be a linear hexyl or octyl aliphatic group or a branched hexyl or octyl aliphatic group. Examples of organometaphosphates include ethylmetaphosphate, propylmetaphosphate, butylmetaphosphate, hexylmetaphosphate and octylmetaphosphate.
The organo-phosphoric acids of the present invention may be utilized in their acidic or salt forms. Examples of salts useful with the present invention are the potassium, sodium, ammonium and aluminum salts and salts formed with alkanolamines such as triethanolamine of the substances identified by Formula 1, Formula 2 or Formula 3.
Organo-acid phosphates are available commercially through, for example, Albright and Wilson Americas of Glen Allen, Va. or may be prepared by procedures known or knowable to those skilled in the art such as those procedures disclosed in U.S. Pat. No. 4,350,645, issued on Sep. 21, 1982 to Kurosaki et al., the teachings of which are incorporated by reference herein. Organopyrophosphates and organopolyphosphates may be purchased from Akzo Nobel or produced according to the procedures that are known or easily knowable to persons skilled in the art. Organometaphosphates may also be produced according to the procedures that are known or easily knowable to persons skilled in the art. Examples of these procedures for synthesizing organopyrophosphates, organopolyphosphates and organometaphosphates are described in Alder, Howard and Woodstock, Willard Chem, Indus., 1942, 51:516, which is incorporated by reference herein.
The aforementioned organo-phosphoric acids, which are the surface treatments of the present invention will be used to treat the pigmentary bases and to form treated pigments. The phrase xe2x80x9ctreated pigmentxe2x80x9d refers to any pigmentary base that has been surface treated or modified. The phrase xe2x80x9corgano-phosphoric acid treated pigmentxe2x80x9d refers to a pigmentary base that has been treated with the reaction products of organic alcohols and P2O5 and/or phosphoric acid; an organo-acid phosphate that may be represented by the above Formula 1; an organopyrophosphate or organopolyphosphate of Formula 2; an organometaphosphate of Formula 3; or a mixture or any of the aforementioned substances. Preferably, the level of organo-phosphoric acid or corresponding salt that is used to treat the pigmentary base ranges from about 0.01 percent to about 5 percent by weight, based on the weight of the pigmentary base; more preferably from about 0.3 percent to about 2.0 percent; and most preferably from about 0.7 percent to about 1.2 percent.
In the organo-phosphoric acid treated pigment, the organo-phosphoric acid may interact with the pigment in a number of manners such as through hydrogen bonding and/or covalent attachments such that the surface treatment resists extraction from the treated pigment. The organo-phosphoric acids that are the reaction products of the organic alcohols, and P2O5 and/or phosphoric acid are generally mixtures of mono- and di-substituted esters in combination with orthophosphoric acid.
The process for making an organo-phosphoric acid treated pigment is easily and flexibly incorporated into existing pigment production processes. Preferably the combining of the pigmentary base and the surface treatment of the invention will occur at a temperature of from about 10xc2x0 C. to about 270xc2x0 C. The specific temperature at which the pigmentary base and the surface treatment are combined is dependent on the step during the pigment production process in which the surface treatment is added.
When an organo-phosphoric acid is used to treat a pigment according to the present invention, a by-product is thought to be water. Because water is the by-product, the organo-phosphoric acid may be added at any one of, or several of, the operations in the pigment production process. For example, the organo-phosphoric acid may be added to a washed filter cake prior to spray drying, to a high intensity milling device or to a micronizer feed prior to or concurrent with micronization. It is not as effective to add the organo-phosphoric acid to a pigment slurry prior to filtration and washing since a portion of the organo-phosphoric acid will be lost upon washing of the pigment depending on the pH. The organo-phosphoric acid can be added to a washed filter cake at normal process operating temperatures. If the organo-phosphoric acid is a solid substance, it may be dissolved in an appropriate solvent, such as water, alcohol, tetrahydrofum, etc., before being added to the pigmentary base. It is desirable to add the organo-phosphoric acid to a fluidized, washed filter cake with agitation in order to assure uniform mixing of the organo-phosphoric acid among the pigment particles. The pH of the fluidized filter cake prior to addition of the organo-phosphoric acid is not critical, and normal operating pH values are acceptable. These values are known or readily knowable to those skilled in the art. If the organo-phosphoric acid is added to a dry pigment such as a spray drier product or micronizer feed, care must be taken to ensure uniform mixing of the organo-phosphoric acid with the pigment powder.
Devices such as a V-shell blender equipped with an intensifier bar for application of the liquid organic or other suitable mixing devices known to those in the art may be used. Alternatively, the organo-phosphoric acid may be metered into the micronizer along with the pigment powder to be ground. Air or steam micronization techniques may be used at temperatures from room temperature up to 250xc2x0 C. or higher as is known or easily knowable to those skilled in the art.
If one adds the organo-phosphoric acid of the present invention to the filter cake or to the micronizer feed, one will minimize the loss of the organic portion of the surface treatment and thereby improve manufacturing efficiency. The treated pigment may be fluid energy milled using steam or air to produce finished pigments that retain high levels of the organo-phosphoric acid compound, which would reduce the overall cost of producing the treated pigment.
When, for example, the pigment is titanium dioxide, organo-phosphoric acid may be added to the untreated titanium dioxide obtained from a production process such as the chloride or sulfate processes. Alternatively, the pigmentary base titanium dioxide may be further treated with additional metal oxides, such as aluminum oxide, silicon dioxide, zirconium oxide and the like, using any process known to those skilled in the art, prior to treatment with the organo-phosphoric acid of the present invention. Additionally, the untreated pigmentary base or the treated pigment may be secondarily treated with polyalcohols such as trimethylolethane and trimethylolpropane or alkanolamines such as triethanolamine.
Once the organo-phosphoric acid treated pigment is formed, it may then be combined with a polymer. The nature of the surface treatment of the present invention allows the treated pigments to be easily incorporated into a polymer matrix. The phrase xe2x80x9cpolymer matrixxe2x80x9d refers to the substance comprising the polymer and the treated pigment. Polymers that may be of use in the present invention include polymers of unsubstituted ethylene monomers, including polyethylene, polypropylene, polybutylene, and copolymers of ethylene with alpha-olefins containing 4 to 12 carbon atoms or vinyl acetate; vinyl homopolymers, acrylic homopolymers and copolymers, polyamides, polycarbonates, polystyrene, acrylonitrile-butadiene-styrenes and polyethers. Other suitable polymer types also include polyvinylchloride, polyurethanes, polysulfones, polyimides, polyesters and chlorinated polyesters, polyoxyethylenes, phenolics, alkyds, amino resins, epoxy resins, phenoxy resins and acetal resins.
The treated pigment may be combined with the polymer and have a loading of up to about 85% by weight, based on the weight of the polymer matrix. Preferably a loading of treated pigment of about 50% to about 85% by weight based on the weight of the polymer matrix is used. This loading may be used as a masterbatch. A xe2x80x9cmasterbatchxe2x80x9d is meant to refer to a mixture of two or more substances that are blended together and then blended with one or more other ingredients that may be the same or different as either of the first two substances. The methods for creating a masterbatch with the treated pigment are known or easily knowable to those skilled in the art. For example, the masterbatch may be created by combining the treated pigment and the polymer using a BR Banbury Mixer.
It has been found, surprisingly and unexpectedly, that the treated pigments of this invention do not generate potentially hazardous or noxious gases when used in combination with the polymeric filler lithopone, which contains combinations of zinc sulfide and barium sulfate. Lithopone, a composition containing zinc sulfide is used as a filler and extender in various polymer compositions. When a TiO2 pigment treated with a phosphorylated polyene is contacted with zinc sulfide at temperatures greater than about 20 to 25xc2x0 C., noxious odors are generated. In contrast, no odors are generated when pigments of the present invention are contacted with zinc sulfide under the same conditions.
It has also been found, surprisingly and unexpectedly that the treated pigments of this invention impart greater lacing resistance to polymers into which they are incorporated. Lacing, which is a believed to be a measure of volatility at specific weight percent pigment loadings and processing temperatures, may manifest as a void or hole in a plastic film.